1. Field of the Invention
This invention relates to a magnetic disc cartridge which accommodates a disc-shaped thin magnetic recording medium, namely, a disc sheet in such a manner that the disc sheet is rotatably supported in the cartridge, and more particularly to a magnetic disc cartridge in which the disc sheet surface cleaning means is improved.
2. Conventional Means
A floppy disc has been proposed in the art as is well known. The floppy disc is manufactured by forming magnetic layers on both sides of a disc-shaped substrate of flexible polyester sheet or the like, so that signals are magnetically recorded on the magnetic layers with a magnetic head while the disc is being rotated. As the floppy disc can be handled with ease and can be manufactured at relatively low cost, it is extensively employed as a recording medium for computers.
A variety of floppy discs have been put to practical use. One example of a floppy disc is a so-called "magnetic disc cartridge" which has been devised in such a manner that a hard case is employed to positively protect the disc sheet and thereby improve reliability. In addition, an opening, through which the magnetic head is brought into contact with the disc sheet, is formed in the hard case and is provided with a slidable shutter in order to protect the disc sheet and to prevent the entrance of dust into the cartridge.
In a magnetic recording medium of this type, a liner is interposed between the disc sheet and the case inner wall confronting the disc sheet. The liner is made of unwoven cloth such as rayon, polyester or the like. The liner is softly brought into contact with the disc sheet while the disc sheet is rotated to clean the disc sheet of fine particles such as dust.
A rectangular lifter made of polyethyleneterephthalate (PET) film is disposed between the liner and the inner wall. The lifter has a fixing part at one end which is secured to the case inner wall, and the remaining part of the lifter is a riser which raises obliquely upwardly to elastically push the liner upwardly. That is, the liner is uniformly brought into contact with the surface of the disc sheet by the lifter so that the disc sheet will be sufficiently cleaned.
In the conventional lifter, the riser and the fixing part are formed by mechanically bending a flat material. As the lifter is secured in the form of a cantilever to the case inner wall, stress due to external force is concentrated at the base of the riser. Furthermore, as the riser is bent in its entirety, when it is used for a long period, it becomes settled. As a result, its pressing force is decreased so that it becomes impossible to sufficiently abut the liner against the disc sheet; that is, the cleaning effect of the liner is gradually decreased.
Especially in the case where the aforementioned magnetic disc cartridge is used for a long period of time, the cartridge may be held at high temperature (usually 50.degree. C. to 60.degree. C.) by the heat generated by the device into which the cartridge is loaded or the frictional heat generated by the rotation of the disc sheet. In the case where the cartridge is stored at high temperature and at high humidity, settling of the lifter made of synthetic resin is expedited, and the elastic force of the lifter is substantially lost. Furthermore, because of the permanent set in fatigue of the lifter, the running torque of the disc sheet is decreased, and it is difficult to maintain the running torque stable.
If the initial pressing force is made large in expectation of the settling of the lifter, then the load of the running torque of the disc sheet is excessively large. The difficulty that the lifter becomes settled may be eliminated by employing a metal lifter; however, use of the metal lifter results in another problem that it is rather difficult to manufacture the metal lifter when compared with the lifter of plastic resin. Magnetic disc cartridges having lifters are described in Japanese early utility model publications Nos. 58-30973, 58-35183, and 60-6939.